The present invention relates to devices and methods for measuring tissue temperature during thermal treatment of a body. More particularly, the present invention relates to a thermal probe comprising a plurality of thermal sensors operable to measure tissue temperatures during thermal treatments such as cryosurgery. Embodiments of the invention enable simultaneous measurements, using a single probe, of temperatures at a plurality of positions within body tissues. A preferred embodiment enables movement of sensors with respect to tissues while the probe is immobilized by being embedded in frozen tissue.
In thermal ablation, and particularly in cryosurgery, collecting information regarding the three-dimensional thermal profile of tissues in and around a treated organ can be extremely important. Efficiency of thermal treatment procedures is enhanced if thermal data is collected from treated tissues, enabling control systems to supply cooling and/or heating at appropriate times and in appropriate amounts. Safety of thermal treatment procedures is also enhanced by temperature data collection from tissues surrounding ablation targets, such data enabling to control cooling or heating to prevent damage to healthy organs in proximity to a treatment target. Thus, for example, collecting of thermal data from tissues in and around a prostate may facilitate protection of a rectum or a urethra positioned near prostate tissue being ablated.
U.S. Pat. No. 6,142,991 to Schatzberger, entitled “High Resolution Cryosurgical Method And Apparatus”, discloses a high resolution cryosurgical method and device for treating a patient's prostate. Schatzberger's method includes the steps of (a) introducing a plurality of cryosurgical probes to the prostate, the probes having a substantially small diameter, the probes being distributed across the prostate, so as to form an outer arrangement of probes adjacent the periphery of the prostate and an inner arrangement of probes adjacent the prostatic urethra; (b) producing an ice-ball at the end of each of said cryosurgical probes, so as to locally freeze a tissue segment of the prostate. The apparatus includes (a) a plurality of cryosurgical probes of small diameter, the probes being for insertion into the patient's organ, the probes being for producing ice-balls for locally freezing selected portions of the organ; (b) a guiding element including a net of apertures for inserting the cryosurgical probes therethrough; and (c) an imaging device for providing a set of images, the images being for providing information on specific planes located at specific depths within the organ, each of said images including a net of marks being correlated to the net of apertures of the guiding element, wherein the marks represent the locations of ice-balls which may be formed by the cryosurgical probes when introduced through said apertures of the guiding element to said distinct depths within the organ. Schatzberger's disclosure includes mention of a single thermal sensor included within a cryoprobe tip, as shown in his FIG. 7. However, the thermal sensor there disclosed is positioned inside the cooling tip of the probe, and therefore is not operable to report temperature of tissues outside the probe during probe operation. U.S. Patent Application No. 2004/0024391 entitled “Apparatus And Method For Protecting Tissues During Cryoablation” by Samuel Cytron et al., filed on Feb. 5, 2004, discloses an apparatus and method for protecting the neurovascular bundle during cryoablation of tissues of the prostate by heating the vicinity of the neurovascular bundle while cooling pathological tissues of a prostate to cryoablation temperatures, thereby cryoablating pathological tissues while protecting the neurovascular bundle from damage. A cryoprobe presented by Cytron also comprises a thermal sensor. Cytron's method for guiding a cryoablation process comprises placing probes containing thermal sensors in intermediate positions around a treated volume.
U.S. Patent Application No. 2005/0143723 entitled “Method For Delimiting Cryoablation By Controlled Cooling”, by Roni Zvuloni et al., filed on Jun. 30, 2005, discloses systems and methods for planning a cryoablation procedure and for facilitating a cryoablation procedure, utilizing integrated images displaying, in a common virtual space, a three-dimensional model of a surgical intervention site based on digitized preparatory images of the site from first imaging modalities, simulation images of cryoprobes used according to an operator-planned cryoablation procedure at the site, and real-time images provided by second imaging modalities during cryoablation. The system supplies recommendations for and evaluations of the planned cryoablation procedure, feedback to an operator during cryoablation, and guidance and control signals for operating a cryosurgery tool during cryoablation.
Methods are provided for generating a nearly-uniform cold field among a plurality of cryoprobes, for cryoablating a volume with smooth and well-defined borders, thereby minimizing damage to healthy tissues.
A thermal sensor probe comprising a plurality of thermal sensors is discussed in U.S. Patent Application 2004/0215294 A1 by Littrup et al. In paragraphs 109-114 Littrup discusses a thin probe resistance thermometers (904) constructed in a linear ray along the probe to provide more than two measurement points. Littrup mentions use of a thin outer coating “(e.g. made of TEFLON®)” to “provide for smooth, non-stick insertion of such a probe”. Littrup does not teach or suggest that such a coating would enable or facilitate displacement of such a probe within frozen tissues. To the contrary, in the same context in which he presents the TEFLON® coating, Littrup teaches use of heating devices to enable removal or displacement of probes within frozen material.
In other words, Littrup's disclosure does not provide a thermal sensor probe capable of movement within frozen tissue. Once Littrup's probe is incorporated into a body of frozen tissue, the positions of thermal sensors within that probe are fixed with respect to that tissue, and cannot be moved or displaced so long as that tissue is frozen. The immobility of the thermal sensors within such a probe thus severely limit the ability of such a probe to provide detailed and accurate thermal information regarding temperatures at a wide variety of positions within and around the iceball created by a cryoablation procedure.
Moreover, it may be noted that it is advantageous for a thermal sensor probe to be as thin as possible, to facilitate insertion and minimize tissue damage by the probe. Requirements for individual electrical connections to sensors within a probe therefore limit the number of sensors which can be included in a probe while that probe yet remains thin. Therefore, there is an upper limit to the fineness of resolution of thermal readings that can be provided by a thin thermal probe containing a plurality of sensors.
Thus, there is a widely recognized need for, and it would be highly advantageous to have, a thermal sensor probe operable to measure temperatures at a plurality of positions within cooled body tissues. It would be particularly useful to have a sensor or plurality of sensors capable of being freely moved and displaced within frozen tissue, according to informational needs of an operator as those needs vary during various phases of a cryoablation operation, even during times when external walls of that sensor probe are immobilized by adhesion to or pressure from frozen tissues contiguous to that probe. Use of such a probe, or a plurality of such probes, particularly within a context providing accurate positioning information with respect to such thermal probes (e.g. Shatzberger's apparatus discussed above) would enable fine resolution of thermal readings from thin thermal probes within treated tissue, and would thus facilitate accurately delimited cryoablation, automatic control of ablation procedures, and accurate prediction of ablation outcomes based on variably positioned real-time temperature readings during an on-going ablation procedure.